1. Field of the Invention
This invention relates to an electronic circuit board case, particularly to a case for housing an electronic circuit board and a method of producing an electronic circuit unit, more particularly to a case for housing an electronic circuit board applied with a coating and a method of producing or manufacturing an electronic circuit unit utilizing the electronic circuit board.
2. Description of the Related Art
Conventional electronic circuit units, such as the one taught by Japanese Laid-Open Patent Application No. 4(1992)-324992 ('992), have been made more compact by vertically stacking an electronic circuit board and power transistors to reduce the footprint of the case housing them. An electronic circuit unit of this type is fabricated by screw-fastening power transistors, passing the power transistor leads through perforations in the electronic circuit board, mounting the electronic circuit board in the case, and finally soldering the power transistor leads.
After electronic components have been mounted on the electronic circuit board, the insulation property of the electronic circuit board is increased by coating the entire electronic circuit board (the side with electronic components and the reverse side) with an insulative paint. As taught by Japanese Laid-Open Patent Application No. 62(1987)-213197 ('197), the coating is conducted simply by dipping the electronic circuit board into coating liquid in a bath. Assembly of the electronic circuit unit is completed by accommodating the coated electronic circuit board in the case.
The electronic circuit unit of the structure set out in '992 requires that the electronic components be soldered after the electronic circuit board has been mounted in the case. Coating of the board is therefore carried out with the electronic circuit board mounted in the case. When the electronic circuit board is coated by dipping it in coating liquid as in the method of '197, therefore, certain coating-prohibited regions of the case (including the edge of the opening contacted by the cover) have to be masked. In addition, when the electronic circuit unit is equipped with a connector, for example, masking is required to prevent the coating liquid from being applied to the connector, particularly the connector pins for connection with external devices. The need for such coating complicates the fabrication process.
In the electronic circuit unit of the structure taught by '992, the electronic circuit board is enclosed by the case. As this makes application of the coating liquid to the heat sink side of the electronic circuit board (the reverse side) difficult, it tends to lower the reliability of the insulation. This electronic circuit unit therefore has room for improvement.
While coating can also be done by spraying, this method also requires troublesome masking.
Regardless of whether the dipping method or the spraying method is adopted, a jig is required for holding the electronic circuit board or the case. This increases cost and complicates the fabrication work.